An operator of a wireless communication system such as UMTS (Universal Mobile Telecommunications System) typically has to administer thousands of base stations. Automatic supervision to the largest extent is mandatory to be able to operate the network with a good quality at reasonable cost.
Different methods are used for the supervision of the antennas and their connection cables/feeders. The most important one is the VSWR supervision. With this method, which is basically known to the man skilled in the prior art, the power Pfwd of a signal travelling to the antenna, the forward signal, and the power Prev of the same signal travelling back from the antenna, the reverse signal, is measured. The ratio VSWR=(1+Prev/Pfwd)/(1−Prev/Pfwd) is monitored, whereby sudden or slow changes exceeding a certain limit indicate a failure somewhere between or at the measurement point and the radiating point.
Performing VSWR measurements for GSM systems is a standard technique. As GSM transmissions through the air are performed in time slots at constant transmission power, it is possible to measure the forward signal to the antenna in a first part of a time slot, and to measure the corresponding reverse signal in a second part of the same time slot.
Using such VSWR measurement devices for CDMA systems, for example UMTS systems, shows unsatisfactory results. A major reason is that the transmission power in the UMTS case is not constant, but depends on the number of user equipments (UE's) to be served. Thus a changing number of user equipments to be served by a base station changes the VSWR ratio and thus distorts a VSWR measurement.